Electrical transmission system including bilateral transistor amplifier



Dec. 8. 1953 w. KOENIG, JR 2,662,123

ELECTRICAL TRANSMISSION SYSTEM, INCLUDING BILATEZRAL TRANSISTORAMPLIFIER Filed Feb. 24, 1951 5 Sheets-Sheet l 2 T LINEAR 2 2 4 POLE [L-kEM/ TTER COLLECTOR e 2 a i BASE Q 2e Fla. 3 26 m I 2/ l2) /l l. :2 12GD FIG. 4 1 1 w W z T z2 z a 1.

/N l E N TOR n4 xos/v/a, JR.

ATTORNEY Patented Dec. 8, 1953 UNITED STATES OFFICE ELECTRICALTRANSMISSION SYSTEM IN- CLUDING BILATERAL TRANSISTOR AM- PLIFIERApplication February 24, 1951, Serial No. 212,639

3 Claims.

This invention relates, in general, to electrical translators; and moreparticularly, to electrical amplifier circuits including transistors.

It has been shown in application Serial No. 96,500, filed June 1, 1949,by R. M. Ryder, and issued concurrently herewith, that a four-poletransistor amplifier can be constructed to give power gain for signalspassing through the circuit in both a forward and a reverse directionand that, under certain conditions, it can be made to give equal powergains in both directions of transmission. In each of the specificcircuit arrangements disclosed by Ryder, a grounded collector transistoris connected between resistive terminations.

Such a circuit is adaptable for use as a twoway amplifier in manyapplications, including coaxial cable systems, but not in systems havingreactive terminations such as loaded cable systems unless certainlimiting conditions are observed.

It is the object of the present invention to provide a bilateraltransistor amplifier having a wider range of utility than the circuitsheretofore devised.

A more specific object of the present invention is to provide anamplifier circuit adapted to give bilateral gain between reactiveterminations.

Another object of the invention is to provide a four-pole circuit inwhich the impedance look ing into one pair of terminals is approximatelythe negative of the load impedance across the other pair of terminals.

In accordance with the present invention, it has been discovered that itis possible to obtain bilateral amplification in a grounded collectortransistor circuit having reactive terminations, provided that, inaddition to the conditions for non-reactive circuits taught by Ryderabove, certain other relationships between the circuit parameters andload impedance obtain. These include, for example, the condition whereinthe terminating impedances at the source and at the load arecharacterized by phase angles of the same sign. Moreover, it is shownhereinafter that the special conditions for optimum gain are realizedwhen these phase angles are made equal and the collector resistance ismade large compared to the other transistor parameters, and theresistive and reactive load components, but approximately half the valueof the forward mutual transimpedance of the transistor.

In addition, the following useful relationship between the terminatingimpedance across each pair of terminals of the grounded collectorcircuit and the impedance looking into the pair of opposite terminalshas been evolved in accordance with the present invention.

If the terminating impedance Z1. between either pair of terminalsapproximates X per cent of the collector resistance Tc, then thenegative impedance looking into the circuit from the opposite pair ofterminals differs from Z1. by approximately K per cent. This fact ismade use of in certain of the disclosed embodiments which relate tosignal repeating circuits of the negative resistance type, comprising atransistor in grounded-collector connection with one pair of terminalscoupled in series with the line, and the other pair of terminals coupledto a balancing network.

The invention in its various ramifications, its objects, and featureswill be better understood from a study of the specification hereinafterwith reference to the attached drawings, in which:

Figs. 1 through 4 are diagrams used in explaining the theory of thepresent invention;

Fig. 5 shows a transmission system including a grounded-collectortransistor bilateral amplifier having reactive terminations inaccordance with the present invention, wherein the bias is locallysupplied;

Fig. 6 shows a variation of the system of Fig. 5, a pair ofgrounded-collector transistor circuits in push-pull relation betweenreactive terminations with a local biasing arrangement;

Fig. '7 shows a transmission system including a bilateralgrounded-collector transistor circuit in accordance with the presentinvention in which bias is supplied over the line;

Fig. 8 shows a two-way electrical transmission system in which atransistor bilateral amplifier circuit having reactive terminationsserves as a negative resistance repeater coupled in series with theline;

Fig, 9 shows a variation of the system of Fig. 5, in which apair ofgrounded collector transistor circuits are connected in push-pullrelation to serve as a negative resistance repeater coupled in serieswith the line;

Figs. 10 and 11 are equivalent circuit diagrams showing the operation ofthe circuits of Figs. 5, 6, and 7; and

Figs. 12 and 13 are equivalent circuit diagrams showing the operation ofthe circuits of Figs. 8 and 9.

Each of the circuits described in Figs. 5 through 9 includes as itsactive element an amplifying device which is known in the art as atransistor, and the construction and operation of which is described indetail in Patent No. 2,525,035, issued October 3, 1950, to J. Bardeenand W. H. Brattain.

The body of the transistor comprises a block of germanium or similarmaterial, the crystalline structure of which is believed :to be alteredby the presence of slight quantities of impurities, as described inBardeen' Brattain above, to provide diiferent conductive types, such as,for example, P-type and N-type. When the major portion of the blockcomprises material of one type, for example, N-type and the surface ofit has been treated to produce a thin barrier layer of P-type, the blockexhibits remarkable amplifying properties. Point contacts, respectivelydenoted the emitter and the collector, make rectifying contact with thetreated surface of the germanium block. A third electrode makes lowresistance contact with the body of the block.

In the specification hereinafter, it will be assumed that the body ofeach of the transistors disclosed comprises N-type germanium having atreated or barrier layer of P-type. However, it is apparent from a studyof Bardeen-Brattain Patent 2,524,035 that transistors comprising a blockhaving a body of P-type material with a barrier layer of N-type materialwill be equally suitable for substitution in the circuits describedhereinafter. In the latter case, the polarity of the biases on theemitter and collector electrode will be reversed with respect to thoseindicated in the drawings and described hereinafter with referencethereto.

As a background for the discussion hereinafter, notations andconventions, as applied to transistor circuits, will be discussedbriefly.

Fig. 1 shows a four-terminal device which has two externally accessiblemeshes. It is conventent to describe such devices as four-poles, eventhough only two of the three possible external meshes are of interest.

Assuming that currents of the form its, 1' 6" are specified arbitrarilyin the two external meshes, where a represents a sinusoidal function totime, then voltages 216'", we appearing across the external terminalpairs are related to the currents by the following set of equations:

1: Z 11i1|12iz (1) B2 21i1+22i2 (2) where the 2's are complex functionsof p.

Equations 1 and 2 are valid under the assumption that the device islinear. The currents i1 and is are taken as the independent variables.

Equations 1 and 2 can be symbolized in matrix form as follows:

Referring to the conventionalized diagram of the transistor in Fig. 2,which shows an emitter electrode, a. collector electrode, and a baseelectrode in contact with a semiconducting body, as describedhereinbefore, the terminals l to the emitter and the base, and theterminals 2 to the collector and the base may be considered ascorresponding to the respective terminals 1 and 2 of the generalizedfour-pole circuit of Fig. 1.

Assuming that Ve represents the direct emitter potential, Ie the directemitter current, Vc the direct collector potential, and In the directcollector current, it has been found that any two of these may be chosenas independent variable and the remaining two expressed as functionsthereof.

Adopting 19, In as independent variable, we have the relation Ve Vc(Ie,I0) (4) Vc '-Ve(Ic, Io) (5) Applying small increments Ie, Is to the icurrent values, one computes the first order increment in the voltagesas follows:

same form as 1 and 2 above, where It is thus apparent that by the choiceof current as an independent variable, the open-circuit impedances Z :1are arrived at as parameters for describing the linear behavior of thetransistor four-pole.

Fig. 3 represents the transistor network of Fig. 2 in the form of anequivalent T network, in which the emitter impedance is represented as29, the collector impedance as Zc, the base impedance as ab, and the netmutual impedance as am. The active element of the transistor is repre--sented as a voltage generator having polarity as shown, whoserelationship to the emitter current is represented as zmz'1, where i1 isthe small signal current into the emitter. As indicated from Fig. 2, theimpedances of the equivalent transistor circuit can be defined in termsof the four-pole impedances developed above:

, cation factor a, defined as providing rs is small compared to Tm. andTc. The basic transistor terminology thus defined will now be utilizedin a brief theoretical discussion of the circuit of the presentinvention.

Consider the circuit indicated in Fig. 4 of the drawings, which is aschematic diagram of the signal paths in a transistor amplifier inaccordsince with the present invention. This comprises an N-typetransistor of the type described hereinabove having a semiconductingbody to which are attached an emitter electrode, a collector electrode,and a base electrode, which are respectively represented as resistancesTe, Tc, and n). On one side of the circuit, the reactive terminatingimpedance Zg is connected between the base electrode Tb and a junctionor ground point. On the other side of the circuit, the reactiveterminating impedance Z1. is connected between the emitter electrode Teand the junction or ground point. The collector electrode is connectedto ground through a circuit of negligible impedance for signal currents.

Under the assumtion that a unity, operation of the circuit shown in theequivalent diagram of Fig. 4 will be briefly analyzed.

Referring to Fig. 4, mesh equations may be set up as follows inaccordance with the wellknown principle of superposition, in order tosolve for VG, the potential drop around the lefthand loop, and V1,, thepotential drop around the right-hand loop.

where Zc. and Z1. represent the impedances between the base and groundand emitter and ground respectively. Note that the symbolism now refersto the mesh of Fig. 4 instead of the open-circuit meshes of Figs. 1, 2,and 3.

From the above equations, the following determinant can be set up:

In order for the system to be stable, A must be greater than zero. Thecondition for equal power gain in both directions is rm=2rc. If this isassumed, A reduces to:

The equations will be simplifier by making Te=Tb. Then,

Now, let Zc. be represented by the complex quantity g+yg, and Zr. berepresented by the complex quantity Z-l-y'Z Then,

Now, let Z/g'=Z/g=(rc-1'b)/(rc+rb), which means that the twoterminations have the same The maximum available power from the sourceZG is The power gain is the ratio of these two quantities, which is Thisis a large gain if n. is large compared to g, l, and Tb.

In the equations for thecircuit mesh shown in Fig. 4, which aredeveloped in the foregoing paragraphs, the terminations are left generalat first, and later specified in terms of resistance and reactancecomponents. It is seen that there occurs a highly favorable cancellationof terms, both among the real and the imaginary components. Note that Teand Tb are small and nearly alike in the average transistor, and can bemade alike, as assumed in the derivation, by means of an externalresistor. Similarly, Tm is. greater than 2% in the average transistorand can be made equal to 2% by building out Tc. The assumed relativemagnitudes of the loads are favorable but not necessary. If ZG isarbitrarily made equal to ZL, it will be found that A becomes larger,but still not so large as to preclude gains greater than unity. As g andl are made smaller than the assumed value, the first term of A becomessmaller and the second one larger. As they are made larger, the secondterm becomes smaller until the product gl' exceeds T11 and thengradually becomes larger again.

If rs is assumed to be very much smaller, say, less than one per cent ofthe product gl, then it will be found that gain is obtained as long asthis product is less than M. If, for example, the components 9 and Z areeach of the order of Tc/3. then a gain of roughly 9- decibels isobtained. If, by either reducing the components Z and g,-or byincreasing the size of To, the former each assume values as low as theorder of Tc/lO, gains of the order of 20 decibels are obtained.

Although the gain does not depend critically .on the angles of theterminations, it is important that they be of the same sign, as Aincreases rapidly, reducing the gain to less than unity, when the signsare dissimilar. It will be apparent from a study of the foregoingequations that, assuming the signs are similar,-the least favorable casefor gain is that in which the phase angles of the terminations equalforty-five degrees.

Referring back to mesh Equations 13 and 1 relating to Fig. 4, Z1, theimpedancelooking back into the terminals at Ze, and Z2, the impedancelooking back into the terminals at Zr. may be shown as follows:

and

Let Tm=2Tc and Te=Tb then and If To is made very large relative to theother circuit parameters, then the following relationships becomeapparent:

In each case, the formulas derived in the preceding paragraphs for theimpedances looking into each pair of terminals, with Zr. and Zc,respectively, connected to the opposite terminals, show that as Tc, thecollector resistance, is made large in proportion to the other circuitparameters, the impedance lookin into one terminal becomes approximatelythe negative of the termination at the other terminal. This condition isfulfilled. as far as the transistor elements are concerned, since Tc,which is assumed to be built out of rm/Z, is of the order of 30,000ohms, and Th and Te are assumed to be of the order of 300 ohms, a ratioof 100:1.

If specific values are substituted in Equations 28 and 28, the followinginteresting relationships are found.

From the above, it is apparent that the following relationship isapproximately true. If the terminating impedance Zn between the emitterand collector terminals in the grounded collector circuit is equal to Xper cent of Tc, then the impedance looking into the base and collectorterminals differs by roughly X per cent from Z1.. A similar relationshipholds between Zc, the terminating impedance between the base andcollector terminals, and the impedance looking into the emitter andcollector terminals.

The circuits shown in Figs. 5, 6, and '7 represent three specificexamples of systems including transistor bilateral amplifiersconstructed in accordance with the teachings of the present invention.

Fig. 5 shows an arrangement using a local source of battery supply forenergizing current. This circuit includes a transistor 50l of the typeshown and described in the Patent 2,524,035 of J. Bardeen and W. H.Brattain, which comprises a block of semiconductor material such as, forexample, N-type germanium. In rectifyin contact with this block is apoint electrode 502 of, for example, phosphor bronze, which isdesignated the emitter; and a similar rectifying point contactelectrode, the collector, 503 disposed at another point on the samesurface of the block as the emitter. For the purposes of the presentapplication, the electrode 503 is connected to the "ground or lowpotential point of the circuit. A third electrode 504, is designated thebase, which comprises a low resistance contact of rhodium or similarmaterial plated onto another surface of the block. The. transistorcircuit is in tandem with, for example, a 19-gauge loaded transmissioncable pair having a phase angle of forty-five degrees, on one sidethrough a first coupling transformer 501, the secondary coil of which isconnected between the emitter electrode and ground in series with signalby-pass condenser 509; and on the other side through an-- other couplingtransformer 508; the primary coil of which is connected between the baseelectrode 504 and ground inseries with signal by-pass con-' denser 510.Each of these transformers may have, for example, a turns ratio of theorder 01 20,000 :135, which is a convenient impedance ratio for theadjacent sections of the described cable; which may comprise part of atransmission system interconnecting terminal stations 5l9, and 520 whichinclude conventional signal transmitting and receiving equipment.Biasing current is furnished by battery 505, which is of the order offorty volts, the negative terminal of which is connected to ground, orthe collector electrode 503, and the positive terminal of which isconnected to the base electrode 504 through one coil of transformer 508,and to the emitter 502 through the 2000 ohm bleeder resistance 50B andone coil of transformer 501. It is apparent that some of the currentflowing through the collector 503 flows through the emitter 502, butmost of it flows through the base 504, thus providing the proper biasesto the transistor elements. In some cases, a retard coil is indicated inseries with the bleeder resistance 506 to keep the signal currents outof the battery supply path. However this is not necessary if theresistance of the bleeder resistor 506 is sufiiciently high.

The relationships between the loads Zr. and Z0 (which are respectivelyrepresentative of the circuits at terminals M9 and 520, the transformers501, 508 and the interconnecting cable sections) and the transistorparameters, are determined in accordance with the teachings in theearlier portions of the specification to give the desired gain, and toprovide the desired impedances looking into the circuit terminations.

Fig. 6 of the drawings shows a circuit which is largely similar to thecircuit shown in Fig. 5 except that it includes two transistors 60! aand B0lb in push-pull arrangement to provide a better balance. In thetwo circuits, elements having corresponding designation in the 500 and600 series of designation numbers, respectively, may be assumed to besubstantially similar. The emitters 602a and 6022) are connected to thetwo terminals of the secondary coil of transformer 501; and the baseelectrodes 604a and 604b are connected to the terminals of the primarycoil of transformer 608, whose center tap is connected to the positivetap of biasing battery 605. The collectors 503a and 60312 are connectedtogether to ground. The transformers 601 and 508 are connected throughrespective cable sections on either side, which are of the typedescribed with reference to Fig. 5, to terminal stations 619 and 620.Here, a with reference to the circuit of Fig. 5, the teachings in theearlier part of the specification apply to the selection of the loadimpedances, and their relation to the transistor parameters.

Fig. '7 shows a circuit in which energizing power for the bilateraltransistor amplifier circuit is supplied over the line.

As in previous embodiments, the relations between the parameters oftransistor TM and the I load impedances are determined in accordancewith the teachings set forth in the earlier part of the specification.

On one side of the circuit of Fig. 7, the impedance Zr. includes thetransformer 101, comprisin a pair of windings connected in seriesbetween the emitter and collector, both inductively coupled to a thirdwinding, which is connected through a transmission circuit of the typedescribed with reference to Fig. 5, to conventional signal transmittingand receiving circuits at terminal H9. On the other side, the impedanceZc includes the transformer 108, comprising two pairs of inductivelycoupled coils, one pair of which is connected in series between the baseand collector of transistor ml; and the second pair of which i connectedthrough a line section to a similar pair of series connected coils oftransformer H4. A third coil of transformer H4 inductively coupled tothe last-mentioned pair is connected through a line section to theconventional signaling circuit at terminal 720.

The transistor MI is coupled with the line through transformer 10?,connected between the emitter and collector electrodes on one side, andtransformer E08 connected between the base and collector electrodes onthe other side. Biasing current for the transistor electrode isfurnished through a repeat-coil arrangement at the terminal station,which comprises potential source 1 N5, of the order of forty volts, thepositive terminal of which is connected through a portion of thewindings of each of repeat coils H4 and 108, and acros thedirect-current connection between the primary and secondary coils oftransformer 708 to the base electrode of transistor 10!; and also fromthe said direct-current connection through the 2000 ohm bleederresistance I03 connected to the center tap of coil I00, and a portion ofthe windings of coil 101 to the emitter electrode 102. The signalby-pass condensers 1H, H2, and H5 are respectively placed in series witha portion of the windings in each of the transformers 101, 108, and H4to provide signal by-pass paths around the high resistance energizingcircuit. The collector 103 is connected to the low potential junction ofone of the coils of each of transformers I01 and 108.

Such applications as described in Figs. 5, 6, and 7 are adaptable foruse in repeaters of the 21 type in which the transistor bilateralamplifier circuit, such as indicated in Fig. 7 including transistor l0l,is connected in tandem with the transmission line which terminates inthe signal transmitting and receiving stations H9 and 120 at its twoends. In thi case, no balancing networks are needed, but the impedancesshould be similar in the two directions, and message signaling currentsby-passed, as shown.

The circuit of the present invention is also adaptable for use as anegative resistance repeater in which case signaling current need not beby-passed, andthe terminating impedances can be dissimilar, but anauxiliary impedance network is needed.

Such a repeater circuit utilizing a transistor as a negative resistanceelement is shown in Figs. 8 and 9 of the drawings. Referring in detailto Fig. 8, transistor 80! is of a type such as described hereinbefore,having an emitter 802, a base 804, and a collector 003 connected toground as in the previously described circuits. This circuit is coupledto the reactive transmission line 82l, through one of the coils 801a ofthe threewinding transformer 80?. The transmission line 82!, which may,for example, be a 19 gauge loaded cable pair, with a phase angle offortyfive degrees, a described before, connects the signal transmittingand receiving circuits at terminal 8l9 with the transmitting andreceiving circuits at terminal 820. The coil 807a is connected betweenthe emitter 8232 and ground in series with the condenser 809, which may,for example, have a value of the order of four microfarads. The baseelectrode 804 is connected through the primary coil of the transformer808 to the collector 803 in series with the four-microfarad by-pascondenser 810. The balancing network 822, which is coupled to the basecircuit through the transformer 800, is so constructed that it has apositive impedance such as to yield the desired negative impedance whenviewed from the line. The negative impedance Z, which is to be insertedin the line, depends on the characteristic of the repeater circuit. Forexample, if the latter is such that the input impedance looking into theemitter and collector terminals is equal to the negative of theterminating impedance connected across the collector and base terminals,then Zn, the characteristic impedance of balancing network 022, shouldbe made equal to the impedance presented across the emitter andcollector electrodes by the line. The balancing network 822 may beconstructed in accordance with the teachings of J. L. Merrill, Jr.,Patent 2,582,498.

A in the previous circuits, bias of approximately forty volts issupplied from the battery 005, the positive terminal of which isconnected through the primary coil of transformer 808 to the baseelectrode 804, and through a bleeder resistance 805, of the order of2000 ohms, and coil 801a of the three-way transformer 00'! to theemitter electrode 802. A variation of this circuit may be made byreversing the connections to the base and emitter electrodes.

A similar and better balanced circuit i shown in Fig. 9 of the drawings,in which the single transistor indicated in Fig. 8 is replaced by a pairof transistor m and 90lb in push-pull arrangement.

In this circuit, the emitters of the respective transistors 90m and 90)are connected to the two terminals of coil 901a which i part of thethree-winding transformer 90'! providing coupling to the line, as in thepreviously described arrangement. The two collector electrodes areconnected together to ground; and the base electrodes are connected toopposite terminals of the primary coil of transformer 908, whichperforms the function of coupling to a balancing network, as in thepreviously described arrangement. Bias is furnished from the positiveterminal of battery 905, which is connected through resistance 906, ofthe order of 2000 ohms, to the center tap of transformer coil 901a forthe emitter electrodes, and directly to the center tap of one coil oftransformer 908 for the base electrodes.

Since it is comparatively simple to provide battery supply for thetransistor from a remote point, the 21-type application is adapted foruse as an unattended repeater.

The equivalent circuit diagrams shown in Figs. 10 to 13, inclusive,supplement the circuit schematics of Figs. 5 to 9, inclusive; andillustrate the following explanation of the method of operation of thedisclosed repeaters.

Fig. 10 is an equivalent diagram of Fig. 5 in which the terminalstations, the two lines and the transformers are now represented simplyby 11 the terminations Ze and Zr. Suppose a signal is coming from theleft, that is, it originates in Zc with the polarity indicated. If thetransistor is regarded simply as a passive network, currents labeled iswill flow in the two meshes in the directions indicated. The presence ofa current in the emitter circuit of the transistor, however, causes avoltage to be generated in the collector circuit of the transistor. Thisvoltage has the indicated polarity and produces currents labeled itflowing as shown in Fig. 11. It will be noted that it is in the samedirection as is in Zc, but is in the opposite direction in ZL. Thecurrent in Zr, however, due to the transistor, is so much greater thanit would have been if the transistor were not present, that there iseffective amplification of the signal from Zc, into ZL, as shownmathematically, in Equations 13 through 25.

A signal coming from the opposite direction is indicated in Fig. 12. Theresultant current in the emitter circuit again produces a voltage in thecollector circuit, this time with the opposite polarity. The resultingcurrents due to the transistor are shown in Fig. 13. Again there isamplification as proved mathematically in the earlier part of thespecification.

It will be obvious that these diagrams, although they bear directly onFig. 5, also apply equally well toFigs. 6, 1,8, and 9. With regard toFig. 8, the network 822 maybe represented by the termination Zr. in Fig.10, and external circuits, viz. the line in Fig. 8, by ZG in Fig. 10. Asnoted before, it in ZG is in the same direction as is in Ze; that is,more current is flowing in Zc than would be flowing if the transistorwere not there. This means that the transistor inserted ahead of Zn actslike a negative resistance because it decreases the effective totalresistance of the combination of Zc and ZL, as was more rigorouslyproved mathematically in Equations 26 through 30. I A similar argumentcan be used in case the transistor is reversed, that is, if ZLrepresents the impedance presented to the transistor by the line as inFig.8, In this case Figs. 12 and 13 apply, and it will be seen that it i'in the opposite direction .from is. A voltage in ZL therefore causes acurrent to flow in the opposite direction from that in whichit wouldflow if the transistor were not present. This is another way of sayingthat the transistor inserted between Zr. and Z6 acts as a negativeresistance.

Bilateral amplification "between reactive loads can-be carried'out inaccordance with the teachings of the present invention in differenttypes of systems, and using other circuit arrangements than thosedescribed herein by way of illustration.

what is claimed is: c c

'1. A'bilate'ral amplifier-for transmittingsignals with substantialpower gains in a forward-direction land in a reverse direction, saidamplifier *in'cludinga serniconductor body having in 'contact therewithan emitter electrode, a collector electrode, and a baseelectrode, afirst load circuit including said "base electrode and said collectorelectrode, said first load circuit having 'a reactive impedance Zc, asecond load circuit including said emitter electrode and"said'coll'ector electrode, said second load'circuit having a reactiveimpedance ZL, said first and second load circuits having a commonportion including said collector electrode, wherein the currentamplifiae'carcs 12 cation factor 'a is greater than unity, wherein thequantity is greater that zero, wherein the phase angles of theimpedanc'es Z1. and Zc are of the same sign, wherein the product of thereal components or impedances Zr. and Zc is substantially less than M,and wherein Tb, re and Te, respectively, represent the base resistance,the collector resistance, and the e'mitter resistance of saidtransistor, and Tm represents the resistive component of the collectortransimpedance.

2. A combination comprising an electrical transmission line having asubstantial reactive component, negative resistance repeating meanscoupled to said line, said negative resistance repeating meanscomprising in combination a transistor having an emitter electrode, abase electrode, a collector electrode and 'a semiconducting body incontact with said electrodes, a first coupling means connected in serieswith signal by-passing means between one of said 'first two electrodesand said collector electrode for coupling said transistor to said line,a second coupling means connected in series with signal by-passing meansbetween the other of said first two electrodes'and said collectorelectrode, a balancing impedance network coupled to 'sa'id't'ransis'torthrough said second coupling means, and means in circuit relation withthe electrodes of said transistor for biasing said electrodes tooperating condition, wherein the impedance looking into said transistorfrom said first coupling means is substantially'equal to a negative unitconstant times the impedance of saidbala'ncing network.

3. A two-way electrical transmission channel including interposed insaid channel at least one two-way semiconductor amplifier, saidamplifier comprising a semiconducting body, an emitter electrode, acollector electrode, and a'ba's'e electrode in contact with saidbody, afirst load circuit connected between said base and collector electrodesand having an impedance that includes a substantial reactive component,and a second load circuit connected between said emitter and collectorelectrodeshaving 'an impedance that includes asubstantial reactivecomponent, wherein at le'ast one of said load circuits comprises saidtwo-way-electrical transmission channel, wherein the impedance lookinginto said transistor from one of said load circuits issubstantiallyequal to a negative unit constant times the impedance of the other ofsaid load circuits, wherein-rm approx imates 27'c, Te approximates rb,and Zc is of the same order of inagnitude as Zr, which is "notsubstantially 'in excess of one per cent of the numerical value of thecollector impedancerc, wherein Zr. and respectively represent theimpedances of said first and second load circuits, wherein Tb and Terespectively represent the base and emitter resistances, and wherein Tmrepresents the resistive component of the-net-mutual transimpedance ofsaid transistor.

WALTER KOENIG, JR.

References Cited-in the file of this patent UNITED STATES rrrrnirrsNumber "Name Date 2,517,960 Barney et'al 'Aug. 8, 1950 2,522,395 0111septic, 1950 2,550,513 Barney Apr. 2'4, 1951 2,585,078 Barney Feb.12,1952

